Poly(vinyl butyral) (PVB) is commonly used in the manufacture of polymer sheets that can be used as interlayers in light-transmitting laminates such as safety glass or polymeric laminates. Safety glass often refers to a transparent laminate comprising a poly(vinyl butyral) sheet, or interlayer, disposed between two sheets of glass. Safety glass often is used to provide a transparent barrier in architectural and automotive openings. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening or the dispersion of shards of glass, thus minimizing damage or injury to the objects or persons within an enclosed area. Safety glass also can be used to provide other beneficial effects, such as to reduce ultraviolet (UV) and/or infrared (IR) light transmission, and/or enhance the appearance and aesthetic appeal of window openings.
Safety glass interlayers have also been used as an important component in automobile head-up display (HUD) systems, which can provide, for example, an instrument cluster image at the eye level of a driver of the automobile. Such a display allows a driver to stay focused on the upcoming road while visually accessing dash board information. One type of interlayer used in such head-up display systems is wedge shaped in vertical cross section. The wedge shape of the interlayer is used to provide the correct light dynamics through the windshield required for a head up display. Unfortunately, as with standard windshields, head up display windshields can also lead to an undesirably high noise transmission level through the windshield.
Accordingly, further improved compositions and methods are needed to enhance the sound dampening characteristics of multiple layer glass panels, and specifically multiple layer glass panels in which a wedge shaped interlayer is used to provide for head-up display capability.